Feedwater System (AE)
Purpose of Feedwater System
take water from the deaerator via the deaerator storage tank, heat it via IP and HP
feedwater heaters and deliver it to the economizer inlet to the boiler
supply water to the two upper and two lower superheater attemperator sprays, the
reheater attemperator spray
supply water to the following desuperheater/steam conditioning valves:
o cold reheat letdown auxiliary steam supply
o main steam letdown auxiliary steam supply
o steam seal desuperheater
System Overview
Two 50% capacity feedwater heater booster pumps (BFBP) and two 50% capacity boiler
feed pumps (BFP) running at full load with recirculation back to deaerator tank
Water quality controlled by injecting neutralizing amine and oxygen scavenger into the
combined suction pipe of the feedwater booster pump
The overall system design is based on the maximum continuous rated (MCR) main steam
flow of 3199472 lbs/hr (including additional requirements for blowdown and
sootblowing, heat balance shows of 3403118 lbs/hr)
Component Description
Major components of the feedwater heater:
Deaerator/Deaerator Storage Tank
Feedwater Booster Pumps
Feedwater Booster Pump Lube Oil System
Boiler Feed Pumps
Boiler Feed Pumps
Boiler Feed Pump Lube Oil System
Feedwater Heaters
Deaerator/Deaerator Storage Tank
Equipment Number ME/MTAE01
Design Outlet Capacity 3196612 pph
Normal Operating Pressure 139.5 psia
Normal Operating Temperature 357
o
F
Spray Nozzles 82
Trays 360
Design Operating Storage Capacity 35850 gals
purpose of the deaerator
o Remove noncondesable gases(dissolved oxygen and carbon dioxide) from the
feedwater as it may produce corrosion and pitting and therefore must be removed
to protect piping, pumps, feedwater heaters and boiler
Employs a two-stage counter flow system of heating and deaerating the feedwater
First stage
o Condensate water
o Self-adjusting spray nozzles
o Preheater section (as uniform spray film)
o Direct contact with the steam atmosphere (instantaneous heat transfer)
o Steam enters the preheater
o Water goes to the tray stack/section (elevated to within 2
o
F)
Second stage (tray section)
o Heated water at saturation temperature
o Flows over the tray stack
o Counter flowing steam
o Feedwater water falls into the bottom of the deaerator to the downcomers
Feedwater Booster Pumps
Equipment Number MPAE001A/B
Type Centrifugal, horizontal, with radially split
casing and double bearing
Stage One
Capacity 3850 gpm
Total developed head 573.9 psi
Minimum flow 1850 gpm
Electric motor driven, 2000 hp, 3570 rpm, 4160Vac
Interlocks which prevent starting the feedwater booster pump:
Deaerator level
Low lube oil pressure
Pump suction valve not fully open
Pump recirculation valve not fully open
Pump suction NPSH low low
Pump bearing temperature high high
Pump is in the red tag mode
Emergency stop has not been reset
Interlocks which trip an operating feedwater booster pump:
Deaerator low low level
Low low lube oil pressure
Pump suction NPSH (Net Positive Suction Head) low low
Pump bearing vibration high high
Activation of the emergency stop
High high motor winding temperature (via multilin)
Pump flow high high (runout protection)
Pump flow low low
Four pump temperature elements for indications, alarms and pump trips
Inboard radial bearing temperature
Outboard radial bearing temperature
o 175F high temp alarm, 185F pump trip
Inner thrust bearing metal temperature
Outer thrust bearing metal temperature
o Alarm at 255F, pump trip at 265F
The motor has two temperature elements
Shaft inboard and outboard bearings
Six pump vibration probes for indication, alarms and pump trips
Inboard bearing x-axis vibration
Inboard bearing y-axis vibration
Outboard bearing x-axis vibration
Outboard bearing y-axis vibration
Thrust bearing axial displacement
Shaft eccentricity (alarm at 10% higher)
Axial vibration of 17 mils and radial vibration of 2.5 mils will cause alarm
Axial vibration of 19 mils and radial vibration of 3 mils will cause pump trip
Six motor stator winding resistance temperature detectors (RTD) connected to multilin for motor
management
AETE 171/271 through AETE176/276
Alarm at 311F high level, 329F high high for pump trip
Running current high alarm at 110A.
Closed cooling water system provides cooling water to each seal cooler at a maximum inlet
temperature of 110F.
Equipped with space heater to prevent condensation.
Feedwater Booster Pump Lube Oil System
Equipment Number MPAE03A/B
Design/Operating Flow Rate 9.4/6 gpm
Design/Operating Discharge Head 75/20 psig
Electric motor-driven, 1hp, 3500 rpm, 480Vac
Reservoir Capacity 40 gallons
Lube Oil System
Auxiliary lube oil pump, with relief valve (at 75psig)
Shaft driven main lube oil pump, with relief valve (at 75psig)
Duplex strainer
Lube oil cooler
Lube oil reservoir
Distributes oil to pump bearings but not to motor bearings.
Motor bearings are self-lubricating from their respective oil reservoirs.
A pressure control valve maintains the supply header pressure at 20psig.
Shaft-driven main lube oil pump runs when header pressure is above 22psig.
Auxiliary lube oil pump will auto start oil header pressure drops to 18psig.
Auxiliary lube oil pump continues to run for 603 sec after BFBP is shut down. (coastdown
completed)
18psig low oil pressure, alarm
16psig low low oil pressure, pump trip
Closed cooling water at greater than or equal to 4gpm, intlet temp at 100F, outlet temp at 114F
Oil supplied to the pump bearings is maintained below 120F
Boiler Feed Pumps
Equipment Number MPAE002A/B
Type Horizontal, double case, centrifugal pump
Stage Eight
Capacity 4050 gpm
Discharge head 2938 psi
Minimum flow 2000 gpm
Electric motor driver, 7600 hp, 3589 rpm, 13.8kV ac
The boiler feed pumps discharge the feedwater at high pressure in order to overcome the
pressure drop within the feedwater system, the economizer, boiler, and main steam steam
system.
Interlocks which prevent starting the boiler feed pump:
Low lube oil pressure
Pump suction valve not fully open
Pump recirculation valve not fully open (at least 40% open)
Pump suction NPSH low low
Pump bearing temperature high high
Pump is in the red tag mode
Emergency stop has not been reset
Interlocks which trip an operating boiler feed pump:
Low low lube oil pressure
Pump is running and flow rate is low low
Flow rate is high high
Neither BFBP is running
BFBP has a high high flow (1 BFBP and 2 BFP operating)
Pump suction NPSH low low
Pump bearing temperature high high
Pump bearing vibration high high
Activation of emergency stop
High high motor winding temperature (via multilin)
Boiler feed pump has three pump temperature elements
Inboard radial bearing metal temperature (175F alarm, 185F trip)
Outboard radial bearing metal temperature (175F alarm, 185F trip)
Inner/outer thrust bearing LO return (160F alarm, 185F trip)
Motor has two temperature elements
Shaft inboard and outboard bearings
Six pump vibration probes for indication, alarms and pump trips
Inboard bearing x-axis vibration
Inboard bearing y-axis vibration
Outboard bearing x-axis vibration
Outboard bearing y-axis vibration
Thrust bearing axial displacement
Shaft eccentricity (alarm at 10% higher)
Axial vibration of 17 mils and radial vibration of 2.5 mils will cause alarm
Axial vibration of 19 mils and radial vibration of 3 mils will cause pump trip
Six motor stator winding resistance temperature detectors
AETE471/571 through AETE476/576
Alarm at high temp of 320F, Trip at high high temp of 328F
High running current of 300A will over current alarm.
Closed cooling water system provides cooling water to each seal cooler at a maximum inlet
temperature of 110F.
Boiler Feed Pumps Lube Oil System
Equipment Number MPAE04A/B
Design/Operating Flow Rate 19.6/16 gpm
Design/Operating Discharge Head 75/20 psig
Electric motor-driven, 2hp, 3500 rpm, 480Vac
Reservoir Capacity 130 gallons
Lube Oil System
Auxiliary lube oil pump, with relief valve (at 75psig)
Shaft driven main lube oil pump, with relief valve (at 75psig)
Duplex strainer
Lube oil cooler
Lube oil reservoir
Motor bearings are self-lubricating from their respective oil reservoirs.
A pressure control valve maintains the supply header pressure at 20psig.
Shaft-driven main lube oil pump runs when header pressure is above 22psig.
Auxiliary lube oil pump will auto start oil header pressure drops to 18psig.
Auxiliary lube oil pump continues to run for 10 min after BFBP is shut down. (coastdown
completed)
18psig low oil pressure, alarm
16psig low low oil pressure, pump trip
Closed cooling water at greater than or equal to 15gpm, intlet temp at 100F, outlet temp at 110F
Oil supplied to the pump bearings is maintained below 120F
Feedwater Heaters
The purpose of intermediate feedwater heaters 5 and 6 and high pressure feedwater heater 7
(MEAE002,3,4) is to use turbine extraction steam to increase temperature as much as possible
before its introduction into the boiler to improve efficiency of steam cycle.
Flow Path and Controls
Main Flow Path
Condensate enters deaerator at 279F, heated by extraction and boiler flash tank steam
Condensate in the deaerator is heated to 353F prior to its use in the feedwater systems.
Deaerator Storage Tank is the collection point for the water and condensed steam that
was supplied to the deaerator heater.
Deaerator storage tank level changes are inticipated by the DCS and modulated by level
control valve (ADLV 402 FC) to maintain normal storage tank level of 98 inches.
Deaerator storage tank normal water level is designed to supply the feedwater booster
pump for 5 minutes in the event of loss of condensate flow to the deaerator.
DA Storage Tank instrumentation
DA level transmitter This signal + total feedwater flow rate signal
to modulate ADLV402
High level alarm at 106 inches
Low level alarm at 80 inches
Close the emergency drain valve at 98 inches
Low Low DA Level Alarm
BFBP Permissive/Trip Switches
Low low level alarm
Trip BFBP
Prevent BFP from starting
At DA level of 18 inches
High DA Level Alarm and Drain Switches High high level alarm
Open emergency drain valve
At DA level of 110 inches
DA high high high level alarm and isolation
switches
Close FWH #5 normal drain valve, extraction
steam line bleeder and motorized valve,
pegging steam line valve,
At DA level of 116 inches
Level indication Local level indication only
Pressure indication
Temperature element
Pressure indication
Pressure transmitter
